Hej since you are Swedish I would recommend you to look at this website, one of the best ones according to me. I have myself bought a PC from them.
If you only need some inside parts I would recommend to look at the "upgrade packages" (Uppgraderingspaket)
For gaming you should choose something like this
http://www.komplett.se/k/ki.aspx?sku=495976#info (RAM+Mobo+CPU)
And if you are looking at a decent graphics card then I would recommend this;
http://www.komplett.se/k/ki.aspx?sku=623768Total; 4.690,00 SEK.
Good budget PC? ^^